If you are using cookie-based authentication and you want to sign out all users (so that they have to re-authenticate), you need to invalidate all of the cookies.
Because the cookies live in the client's browser, you cannot simply clear them like you would with session-based authentication. Instead, you need to replace the session token used to create all those cookies.
First, get a new token:
$ bundle exec rake secret
538696c1399ff182486e09980ba915d098b8fb23a3ace42c3eea0ab51b18fdff7895cd620f32b263d10d25c2fdba16647f4d8632e9032eccef7406e1ad9cba09
Then, replace the current secret_key_base
value with that new secret token
wherever it is
stored
in the production environment.