1.) Purge entire Cache
2.) Request a page in shop that is not exluded from being cached.
3.) Check cache header like before
4.) If cache header is miss, everything is okay.
5.) If cache header is hit, wait a few seconds and request same page again. If cache header ist still hit, something is wrong and you should open support ticket or start from 1.)
Cache header is the only way to verify cache status of a URL. If you have access to CLI you can remove cached files from disk. Quick and fast.