I left my account logged in on a computer owned by someone else, they have decided to troll and so ive changed my password and cleared my session. I verified with SE openid that they did not log in after that, but they still have access to my chat account. How do I handle this situation, and can password change trigger an actual working global cookie invalidation in the future?
It sounds like you left multiple services logged in - your email (required to confirm a Stack Exchange OpenID password change), SE OpenID, SE sites, possibly others.
The best defense is, honestly, to never leave yourself logged in on someone else's computer. Incognito browser sessions come in very handy for this sort of thing.
Now that the damage has been done, I see that the offending credential has been removed from your profile, and your login sessions have been cleared. When you have your logins secured, let us know and we'll lift your (currently network-wide) suspension.