I'm not sure I'm following what you're saying a 100%, but based on this [1] i don't think the fingerprint hash is ever in memory. The TouchID camera sends the fingerprint hash directly to the secure enclave, where it is compared to the one saved there, and then the secure enclave sends a yes or no to memory, at least that's my interpretation

1. http://support.apple.com/kb/HT5949?viewlocale=en_US&locale=e...