Instructions
Turn on the PS3 system you would like to disable. You have to disable the account from the system in question.
Sign into your PS3 account.
Scroll to "Account Management" and select "Activate System."
Select "PS3" and then "Game Content."
Highlight "Deactivate" and hit the confirmation button to deactivate your account on this specific PS3 system.
Complete these steps on every extra system that holds your user data.