If you have users logged in then there is a session connected
with their account, when they log out that session is deleted. So
if you know how your sessions are set and with what kind of named
variables, then you can check on that variables and link them to
the logged in user data that is in the db.
For example, when there is a session set with:
<cfset SESSION.username=username from database>
then there is a session.username variable active which holds
the value of the username from the database.
These values corresponds which enable you to match
those.