Yes, CIRCUMSCRIBE is a Scrabble word!

Letter values in Scrabble US: C 3, I 1, R 1, C 3, U 1, M 3, S 1, C 3, R 1, I 1, B 3, E 1.

Is it a valid word?

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

draw a line around
restrict or confine, "I limit you to two visits to the pub a day"
to draw a geometric figure around another figure so that the two are in contact but do not intersect