Yes, COCA is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, C 3, A 1.

Is it a valid word?

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

a South American shrub whose leaves are chewed by natives of the Andes; a source of cocaine
United States comedienne who starred in early television shows with Sid Caesar (1908-2001)
dried leaves of the coca plant (and related plants that also contain cocaine); chewed by Andean people for their stimulating effect

Also: erythroxylon coca, coca plant, imogene coca.