If it was a straight-up conviction (no conditional plea, or anything like "diversion"), it cannot be expunged under Tennessee law (the exception being that if it occurred before July 1, 2005, you were under 21, and had no prior record).

It is federal law that prohibits you from owning a firearm with a domestic violence conviction. The only way to even potentially recover your gun rights would be to petition the governor for a pardon. Even then, due to the way the Tennessee pardon power has been interpreted, there is some debate as to whether or not that would allow you to own a gun under federal law.