In some wikis, if we block a user, we want to kill of their sessions and log them out (because they aren't allowed to edit their talk page, because requesting unblock isn't a rule on the wiki)...
invalidateUserSessions.php can be used to invalidate sessions, but not everyone always has shell access etc
Not sure if this should live in MW core, behind some feature flag... Or somewhere else?
Should be relatively simple to code though
(This user should not be able to log in to the wiki, otherwise they may easily circumvent such action)