--- a/tools/tryselect/tasks.py
+++ b/tools/tryselect/tasks.py
@@ -1,15 +1,17 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 from __future__ import absolute_import, print_function, unicode_literals
 
+import hashlib
 import os
+import shutil
 import sys
 
 from mozboot.util import get_state_dir
 from mozbuild.base import MozbuildObject
 from mozpack.files import FileFinder
 
 import taskgraph
 from taskgraph.generator import TaskGraphGenerator
@@ -44,17 +46,23 @@ def invalidate(cache, root):
 
     if tmod > cmod:
         os.remove(cache)
 
 
 def generate_tasks(params, full, root):
     params = params or "project=mozilla-central"
 
-    cache_dir = os.path.join(get_state_dir()[0], 'cache', 'taskgraph')
+    # Try to delete the old taskgraph cache directory.
+    old_cache_dir = os.path.join(get_state_dir()[0], 'cache', 'taskgraph')
+    if os.path.isdir(old_cache_dir):
+        shutil.rmtree(old_cache_dir)
+
+    root_hash = hashlib.sha256(os.path.abspath(root)).hexdigest()
+    cache_dir = os.path.join(get_state_dir()[0], 'cache', root_hash, 'taskgraph')
     attr = 'full_task_set' if full else 'target_task_set'
     cache = os.path.join(cache_dir, attr)
 
     invalidate(cache, root)
     if os.path.isfile(cache):
         with open(cache, 'r') as fh:
             return fh.read().splitlines()
 

--- a/tools/tryselect/test/setup.sh
+++ b/tools/tryselect/test/setup.sh
@@ -2,17 +2,20 @@ export topsrcdir=$TESTDIR/../../../
 export MOZBUILD_STATE_PATH=$TMP/mozbuild
 
 export MACHRC=$TMP/machrc
 cat > $MACHRC << EOF
 [try]
 default=syntax
 EOF
 
-cachedir=$MOZBUILD_STATE_PATH/cache/taskgraph
+calculate_hash='import hashlib, os, sys
+print hashlib.sha256(os.path.abspath(sys.argv[1])).hexdigest()'
+roothash=$(python -c "$calculate_hash" "$topsrcdir")
+cachedir=$MOZBUILD_STATE_PATH/cache/$roothash/taskgraph
 mkdir -p $cachedir
 
 cat > $cachedir/target_task_set << EOF
 test/foo-opt
 test/foo-debug
 build-baz
 EOF