It is usually fine if a dog is bitten by a domestic cat, because domestic cats generally do not carry rabies virus. If a dog is bitten by a wild cat, and the bite bleeds or the skin is broken, it is best to clean the wound immediately. Disinfect the dog, and then send the dog to a pet hospital for a rabies vaccine to avoid being infected with the rabies virus; if it is not bitten, it will be fine, and you only need to clean the wound.