You still have access to the site (1 minute)
Step 1 | Access License Screen
-> On the old site, go to the license settings menu.
Step 2 | Deactivate on old (existing) domain
-> Click the red deactivate license button
You don't have access to the site anymore (2 minutes)
Step 1 | Login into the Member's Portal.
Step 2 | Deactivate the license
-> Find your domain and press 'Remove'