When I go to logout, it says

You have profiles on the following domains within our network:

stackexchange.com
stackoverflow.com
superuser.com

Clicking Log Out will log you out of the following domains on this device:

stackexchange.com
stackoverflow.com
superuser.com

If you're on a shared computer, remember to log out of your Open ID provider (Facebook, Google, Stack Exchange, etc.) as well.

So how do I log out on all devices?

Basically, I accidentally did not log out on a computer that is now out of my control. I only logged in via Stack Exchange's login:

Now I want to ensure that anyone who happens to get access to that machine cannot log out. How can I do this?

_{Note: There are a lot of questions regarding logging out, but it's not clear because they say "clear cookies" or "default is to log out of all devices," but clearly I cannot do the first, and Stack Exchange contradicts the second. I want to know what really happens; perhaps a canonical Q&A would be appropriate for this topic}