Actually there's one thing I forgot, there is one feature in Flarum where all sessions are cleared, it's the explicit logout.
If you click the logout button, all your active sessions on all devices are terminated.
If the session expires naturally, other sessions are not terminated.
You might be able to manually trigger this with a javascript call to the logout endpoint. The CSRF token needs to be attached to the request for this to require no interaction from the user.
Once we have a proper session management UI, this behavior will probably be changed because it doesn't actually make much sense to always end all sessions if there's a different button available to do exactly that.
