  We obtained the global persistence exponent $\theta_g$ for a continuous spin
model on the simple cubic lattice with double-exchange interaction by using two
different methods. First, we estimated the exponent $\theta_g$ by following the
time evolution of probability $P(t)$ that the order parameter of the model does
not change its sign up to time $t$ $[P(t)\thicksim t^{-\theta_g}]$. Afterwards,
that exponent was estimated through the scaling collapse of the universal
function $L^{\theta_g z} P(t)$ for different lattice sizes. Our results for
both approaches are in very good agreement each other.
