The earth brewling is the only unit which gains spell immunity via a passive ability.

It would be an interesting an unique interaction. This would allow Scepter Demonic Purge to make the Earth brewling more vulnerable, and it would be the only ability able to disable this passive ability. Silver Edge cannot pierce spell immunity, so it doesn't get to disable it in the first place. Doom's Doom, although applying Break and being able to pierce, is not castable on ancients, so it could not be used to disable the earth's spell immunity, leaving Demonic Purge as the only ability. For 5 seconds, you would be able to Dagon that Earth element, or silence and knock it back with Gust. But you are commiting a Demonic Purge charge for it.