To be incredidably drunk, beyond the means of any human being.
It can also mean: broken beyond the means of human capabilities of repair. Or to describe sex one has had which is beyond human comprehension.
The word originated from the character of the incredible Jack Reacher, created by author Lee Child. The word is almost exclusive to Lurgan, Northern Ireland.
"I was absolutely reachered last night!"
David: What the dickens happened that chair?
Andrew: Ah, sorry Davy. I pure reachered it.
Colin: What happened you last night, like?
Andrew: Haha! Reachered!