While Command-Option-[numpad]/ work great for "Purge All Memory" (aka Menu -> Edit -> Purge -> All Memory),
I was stumped trying to find (or even create) one for it's near neighbor "Purge All Memory & Disk Cache"
Wasn't able to even find the second option listed in the Adobe Preferences file. Any ideas?
It's not an option and you can't make a custom one to do it. Basically if you don't see a keyboard shortcut in a menu item you can't write a custom shortcut to accomplish the task.
I think it sounds like a good time to put in a feature request.
The JS Command is
(Thanks to at Alex11G's answer at https://forums.adobe.com/thread/1506544)
Setting up keyboard shortcuts to external JSX thanks to How to Run After Effects Scripts with Keyboard Shortcuts
But still worth a feature request!