Return all cache records, delete caches with prefixed keys
Not without some brute-force cracking.

The keys you pass into CFileCache's set and get methods are an md5 hash of your key prepended with your Craft installation's appId (which by default is a randomly generated string).

So with a key of testKey, that could end up as a value of 3f8b3c45a9c6f395d02b930f18910a92.  For CFileCache, that value ends up being the file name of the cache file and gets put in craft/storage/runtime/cache/3f8b3c45a9c6f395d02b930f18910a92.bin.

Later, when you call get and pass in the key of testKey, it goes through the same process and checks to see if a file named 3f8b3c45a9c6f395d02b930f18910a92.bin exists.  If it does, it knows there is a match.

As you can see, there's no way to find that match without knowing the key ahead of time (unless you brute-force cracked md5, which is doable, but probably not practical for your use-case).