diff --git a/zerver/lib/actions.py b/zerver/lib/actions.py
index 012ea08182..48d281e899 100644
--- a/zerver/lib/actions.py
+++ b/zerver/lib/actions.py
@@ -3,6 +3,7 @@ from __future__ import absolute_import
 from django.conf import settings
 from django.core import validators
 from django.contrib.sessions.models import Session
+from zerver.lib.cache import update_user_profile_cache
 from zerver.lib.context_managers import lockfile
 from zerver.models import Realm, RealmEmoji, Stream, UserProfile, UserActivity, \
     Subscription, Recipient, Message, UserMessage, valid_stream_name, \
@@ -138,6 +139,29 @@ def delete_all_user_sessions():
     for session in Session.objects.all():
         delete_session(session)
 
+def active_humans_in_realm(realm):
+    return UserProfile.objects.filter(realm=realm, is_active=True, is_bot=False)
+
+def do_deactivate_realm(realm):
+    """
+    Deactivate this realm. Do NOT deactivate the users -- we need to be able to
+    tell the difference between users that were intentionally deactivated,
+    e.g. by a realm admin, and users who can't currently use Zulip because their
+    realm has been deactivated.
+    """
+    if realm.deactivated:
+        return
+
+    realm.deactivated = True
+    realm.save(update_fields=["deactivated"])
+
+    for user in active_humans_in_realm(realm):
+        # Don't deactivate the users, but do delete their sessions so they get
+        # bumped to the login screen, where they'll get a realm deactivation
+        # notice when they try to log in.
+        delete_user_sessions(user)
+        update_user_profile_cache(None, instance=user, update_fields=None)
+
 def do_deactivate_user(user_profile, log=True, _cascade=True):
     if not user_profile.is_active:
         return
diff --git a/zilencer/management/commands/deactivate_old_realms.py b/zilencer/management/commands/deactivate_old_realms.py
new file mode 100644
index 0000000000..805a5f20e1
--- /dev/null
+++ b/zilencer/management/commands/deactivate_old_realms.py
@@ -0,0 +1,17 @@
+from __future__ import absolute_import
+
+from django.core.management.base import BaseCommand
+
+from zerver.lib.actions import do_deactivate_realm
+from zerver.models import get_realm
+
+domains_to_deactivate = """"""
+
+class Command(BaseCommand):
+    help = """One-off script to deactivate our old realms."""
+
+    def handle(self, *args, **options):
+        for domain in [elt.strip() for elt in domains_to_deactivate.split("\n")]:
+            print "Deactivating", domain
+            do_deactivate_realm(get_realm(domain))
+        print "Done!"