Enterprise Mode site list and manual override

I have a small question / issue when using Enterprise Mode.

We have enabled it using GPO by specifying both a site list and the Enable settings for manual override. This works fine but I don't know how to reset the manual override if somebody flicks the EM mode for a specific site.

I just want to tell IE to forget all manual overrides and apply the sitelist as delivered.

I tried to look in the registry, in the %AppData% fodler, even cleared the IE cache but IE still remembers the user overrides.

Any help will be really appreciated.

Thanks, Nic.