When a given user logs out, you can clear his/her cookie in order to allow different users to share a browser without mixing up their session data. Calling clearUserCookie will clear the cookie of the identified user. The next started session from this browser will be associated with the guest user that used your app before you called identify.
sessionstack('clearUserCookie'); // Clear identified user cookie
If you need each new session to be associated with a new guest user - pass true as the first argument to clearUserCookie.
sessionstack('clearUserCookie', true); // Clear identified user cookie and guest user cookie