Yes, THENCE is a Scrabble word!

Letter values in Scrabble US: T 1, H 4, E 1, N 1, C 3, E 1.

Is it a valid word?

THENCE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

from that place or from there
from that circumstance or source
(used to introduce a logical conclusion) from that fact or reason or as a result