Yes, CORNICES is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, R 1, N 1, I 1, C 3, E 1, S 1.

Is it a valid word?

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

a decorative framework to conceal curtain fixtures at the top of a window casing
a molding at the corner between the ceiling and the top of a wall
the topmost projecting part of an entablature

Also: valance board.