Let \( X \) and \( Y \) be two independent random variables with the cumulative distribution functions \[ \begin{array}{l} F_{X}(x)=1-\left(\frac{3}{4} ight)^{x}, \quad x=1,2,3, \cdots \\ G_{Y}(y)=1-\left(\frac{2}{3} ight)^{y}, \quad y=1,2,3, \cdots, \end{array} \] respectively. Let \( Z=\min \{X, Y\} \). Then, the probability \( P(Z \geq 6) \) is (A) \( \frac{1}{64} \) (B) \( \frac{1}{32} \) (C) \( \frac{63}{64} \) (D) \( \frac{31}{32} \)