How do I clear caches (app, individual apps, Dalvik, ART if possible) via ADB?
Using apps, recovery, or doing it through Settings are not options for me. Also, my phone is not rooted.
ADB is close, but things like
adb shell pm clear <package_name> to clear caches (and data, oops) from selected apps requires root (as would clearing Dalvik cache). But there's a similar approach to just wipe out all app caches (not Dalvik/ART, though):
fastboot erase cache would do that with the device booted into the bootloader. Details can be found e.g. here: Useful ADB and Fastboot Commands and How to Use them.