I managed to do that this week.
I don't know why deleting the session didn't work, cause that's what I did, but you need something else on the form (client-side) to quickly force the browser to jump ship.
I did this by embedding a micro ticker/timer that does polling to the application server. As soon as the client side gets a response, it redirects the client to the login screen.
Try showing the new form in the same microflow before the logout java call