defaults delete domain is not working

I'm trying to clear out the defaults for an app I'm working on.

defaults read com.mycompany.Foo

That prints a bunch of stuff.

defaults delete com.mycompany.Foo

Silent.

defaults read com.mycompany.Foo

It's all still there. Why?

defaults delete com.mycompany.Foo specificKey

This appears to work. But I don't want to go through key by key. I'd like to delete the entire domain.