whoisgregg - 4:02 pm on Apr 12, 2012 (gmt 0)
You can force the key cache to be restructered by changing the size of the key_buffer_size. These queries change it to 2MB and then restores it to it's default value:
SET GLOBAL key_buffer_size = 2097152; SET GLOBAL key_buffer_size = DEFAULT;
Unfortunately, to really make sure you've destroyed every possible cache layer you practically have to reset your server. :/
If this doesn't help, maybe looking at the query itself will reveal another avenue to explore.