Yes, CONSISTENCY is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, N 1, S 1, I 1, S 1, T 1, E 1, N 1, C 3, Y 4.

Is it a valid word?

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

the property of holding together and retaining its shape
a harmonious uniformity or agreement among things or parts
logical coherence and accordance with the facts
(logic) an attribute of a logical system that is so constituted that none of the propositions deducible from the axioms contradict one another

Not playable in Scrabble US: EUBSTANCE.