For a block diagonal matrix $\begin{pmatrix} A & 0 \\ 0 & B \end{pmatrix}$ where $A$ is $2 \times 2$ with $\det(A) = 3$ and $B$ is $2 \times 2$ with $\det(B) = 2$, what is the determinant of the full $4 \times 4$ matrix?