Emptying Safari cache

Safari and Mac cache are two different things.

In Safari Preferences : Advanced tab : [√] Show Develop menu in menu bar. Once you have done that, you can press the option+command+e keyboard shortcut, the Develop menu bar item will flash blue, and your Safari Cache has been emptied.

There is little need to empty the Mac System cache, though booting into Safe Boot mode will do that as part of other house-keeping activies unique to this boot mode. Reboot normally afterward. I rarely use Safe Boot myself, and then only as part of a diagnostic process, as we often recommend in these communities.

Why do you want to empty cache?

Generally there is hardly ever a valid reason to do that for the system will only reload it again.