If $$x^3 + y^3 + z^3 = 3(1 + xyz), P = y + z - x, Q = z + x - y$$ and $$R = x + y - z,$$ then what is the value of $$P^3 + Q^3 + R^3- 3PQR?$$

A

9

B

8

C

12

D

6