diff --git a/cylc/flow/network/scan.py b/cylc/flow/network/scan.py
index 7c8116b1a70..c929c2079a7 100644
--- a/cylc/flow/network/scan.py
+++ b/cylc/flow/network/scan.py
@@ -238,7 +238,10 @@ def _scan_subdirs(listing: List[Path], depth: int) -> None:
                 )
 
     # perform the first directory listing
-    scan_dir_listing = await scandir(scan_dir)
+    try:
+        scan_dir_listing = await scandir(scan_dir)
+    except FileNotFoundError:
+        return
     if scan_dir != cylc_run_dir and dir_is_flow(scan_dir_listing):
         # If the scan_dir itself is a workflow run dir, yield nothing
         return
diff --git a/tests/functional/cylc-clean/00-basic.t b/tests/functional/cylc-clean/00-basic.t
index f7fd40c1700..1f4cec84984 100644
--- a/tests/functional/cylc-clean/00-basic.t
+++ b/tests/functional/cylc-clean/00-basic.t
@@ -21,7 +21,7 @@
 if ! command -v 'tree' >'/dev/null'; then
     skip_all '"tree" command not available'
 fi
-set_test_number 8
+set_test_number 10
 
 # Generate random name for symlink dirs to avoid any clashes with other tests
 SYM_NAME="$(mktemp -u)"
@@ -94,7 +94,7 @@ ${TEST_DIR}/${SYM_NAME}/work/cylc-run/${CYLC_TEST_REG_BASE}
             \`-- work
 __TREE__
 # -----------------------------------------------------------------------------
-TEST_NAME="cylc-clean"
+TEST_NAME="clean"
 run_ok "$TEST_NAME" cylc clean "$WORKFLOW_NAME"
 dump_std "$TEST_NAME"
 # -----------------------------------------------------------------------------
@@ -109,5 +109,11 @@ ${TEST_DIR}/${SYM_NAME}/log/cylc-run/${CYLC_TEST_REG_BASE}
 \`-- leave-me-alone
 __TREE__
 # -----------------------------------------------------------------------------
+TEST_NAME="clean-non-exist"
+run_ok "$TEST_NAME" cylc clean "$WORKFLOW_NAME"
+dump_std "$TEST_NAME"
+cmp_ok "${TEST_NAME}.stdout" << __EOF__
+INFO - No directory to clean at ${WORKFLOW_RUN_DIR}
+__EOF__
+# -----------------------------------------------------------------------------
 purge
-exit
diff --git a/tests/integration/test_async_util.py b/tests/integration/test_async_util.py
deleted file mode 100644
index 6c9bfaa565e..00000000000
--- a/tests/integration/test_async_util.py
+++ /dev/null
@@ -1,41 +0,0 @@
-# THIS FILE IS PART OF THE CYLC WORKFLOW ENGINE.
-# Copyright (C) NIWA & British Crown (Met Office) & Contributors.
-#
-# This program is free software: you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation, either version 3 of the License, or
-# (at your option) any later version.
-#
-# This program is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <http://www.gnu.org/licenses/>.
-
-from pathlib import Path
-from shutil import rmtree
-
-import pytest
-
-from cylc.flow.async_util import scandir
-
-
-@pytest.fixture()
-def directory(tmp_path):
-    """A directory with two files and a symlink."""
-    (tmp_path / 'a').touch()
-    (tmp_path / 'b').touch()
-    (tmp_path / 'c').symlink_to(tmp_path / 'b')
-    yield tmp_path
-    rmtree(tmp_path)
-
-
-async def test_scandir(directory):
-    """It should list directory contents (including symlinks)."""
-    assert sorted(await scandir(directory)) == [
-        Path(directory, 'a'),
-        Path(directory, 'b'),
-        Path(directory, 'c')
-    ]
diff --git a/tests/integration/test_scan.py b/tests/integration/test_scan.py
index cef762c394e..94edbfc9b29 100644
--- a/tests/integration/test_scan.py
+++ b/tests/integration/test_scan.py
@@ -250,6 +250,13 @@ async def test_scan_nasty_symlinks(run_dir_with_nasty_symlinks):
     ]
 
 
+async def test_scan_non_exist(tmp_path: Path):
+    """Calling scan() on a scan_dir that doesn't exist should not raise."""
+    assert await listify(
+        scan(scan_dir=(tmp_path / 'HORSE'))
+    ) == []
+
+
 async def test_is_active(sample_run_dir):
     """It should filter flows by presence of a contact file."""
     # running flows
diff --git a/tests/unit/test_async_util.py b/tests/unit/test_async_util.py
index 13cda504b48..17823817dbe 100644
--- a/tests/unit/test_async_util.py
+++ b/tests/unit/test_async_util.py
@@ -16,13 +16,15 @@
 
 import asyncio
 import logging
+from pathlib import Path
 from random import random
 
 import pytest
 
 from cylc.flow.async_util import (
     pipe,
-    asyncqgen
+    asyncqgen,
+    scandir,
 )
 
 LOG = logging.getLogger('test')
@@ -238,3 +240,23 @@ async def test_asyncqgen():
         ret.append(item)
 
     assert ret == [1, 2, 3]
+
+
+async def test_scandir(tmp_path: Path):
+    """It should list directory contents (including symlinks)."""
+    (tmp_path / 'a').touch()
+    (tmp_path / 'b').touch()
+    (tmp_path / 'c').symlink_to(tmp_path / 'b')
+
+    assert sorted(await scandir(tmp_path)) == [
+        Path(tmp_path, 'a'),
+        Path(tmp_path, 'b'),
+        Path(tmp_path, 'c')
+    ]
+
+
+async def test_scandir_non_exist(tmp_path: Path):
+    """scandir() should raise FileNotFoundError if called on a path that
+    doesn't exist."""
+    with pytest.raises(FileNotFoundError):
+        await scandir(tmp_path / 'HORSE')