I'm trying to erase all app-caches via the official adb-shell from the SDK-Toolkit without having to root my phone. Does the command
fastboot erase cache
only deletes app-caches or does it remove app data and general data on the mobile harddrive too?
Check the info on fastboot tag-wiki.
Fastboot erase cache should just erase the cache partition (check the output from that command).
To delete the app data there is another command:
fastboot erase data
But be careful with the commands you use. You could end up with unwanted results. Cheers.