Yes, EXARCHS is a Scrabble word!

Letter values in Scrabble US: E 1, X 8, A 1, R 1, C 3, H 4, S 1.

Is it a valid word?

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

a bishop in one of several Eastern Orthodox Churches in North America
a bishop in eastern Christendom who holds a place below a patriarch but above a metropolitan
a viceroy who governed a large province in the Roman Empire