Quick Cache Pro is not clearing cache for multiple sites/domains e.g. alias domains.

Referencing Ticket: Ticket # 9371

According to @jaswsinc:

That is to be expected. ZenCache only clears the cache for the currently configured domain in a WordPress installation. The only way it can clear multiple sites is if you run it in a Multisite Network installation and click the "Wipe" button that is presented whenever you are running a Multisite Network

Having said that, whenever ZenCache automatically wipes the cache, everything is dealt with (for both domains), but unless you're running a Network, the Clear Cache button will not handle this gracefully I'm afraid.