It's a bit tricky because "indomitable" doesn't seem to relate to a house at first glance. Here's how the connection works:
* domus evolved to dominus, meaning "master" or "lord".
* dominus was then used to describe someone who "rules" or "controls" something.
* indomitable means "unable to be subdued or overcome". Therefore, an indomitable spirit is one that cannot be controlled or mastered.
So, even though it's not immediately obvious, the Latin root domus is connected to the idea of control and ultimately, the lack of it.