Screw holding A down while rebooting, this way works and without reboot.
Go to the system blade and then select memory.
Highlight HD (don't select, just highlight), press Y, and then press X,X,Left Bumper, Right Bumper, X,X.
Once you do this a messsage will appear saying: Do you want to perform
maintenance on your Xbox 360 storage devices?
This will clear your cache but it will also clear game updates (not downloads, just update patches).
Dunno how he found it, but thank my brother (en sabah nor) for that one