  We prove Cardy's formula for rectangular crossing probabilities in dependent
site percolation models that arise from a deterministic cellular automaton with
a random initial state. The cellular automaton corresponds to the
zero-temperature case of Domany's stochastic Ising ferromagnet on the hexagonal
lattice H (with alternating updates of two sublattices); it may also be
realized on the triangular lattice T with flips when a site disagrees with six,
five and sometimes four of its six neighbors.
