Thanks. I forgot to state the version i am dealing with — it's quite old at this point: 3.4.2
If you check the wp_usermeta table, you should see an entry called session_tokens, which contains a user's active session information.
I don't see the session_tokens meta_key entry in wp_usermeta. Has this been added in newer versions than mine? (I did make sure some user is logged in at the time I checked, and I checked across all "user_id" rows)