Crack hitting a domain having the same elastic properties but different fracture toughness (due, for example, to thermal processing) is considered. The focus is on the choice between crack deflection by the domain and crack penetration into it. This choice is controlled by two factors: the angle at which the crack approaches the domain and the fracture toughness contrast. This problem is motivated, in particular, by protecting a material against crack propagation in certain undesirable directions, via deflecting a crack by such domains.