Mischna zu Wajikra 2:6

In the case of a stone in a corner, when the stone is taken out it, he must take it all out; But when [the house is] torn down he tears down his own [part] and leaves that which belongs to his neighbor. Thus it follows that there is a greater stringency for taking out than for tearing down. Rabbi Elazar says: if a house is built of rows of head stones and small stones, and a nega appears on a head stone, all of it must be taken out; but if it appeared on the small stones, he takes out his stones and leaves the others.