How is a house (carpets, walls, doors) in which a dog was kept purified?

The basic principle concerning objects is purity. They do not become impure except by certain contact with impurity. If you are certain that a dog's saliva has come into contact with a specific spot in the house, then that spot must be washed seven times, by analogy with its lapping. However, if the impurity is from the dog itself, but not its saliva, then it is removed like any other impurity. But if you are not certain, then you are not obligated to wash it.