Rebuilding dependencies in Xcode - what are the rules?

Question

CMake

By what rules does Xcode mark the need to rebuild the entire target?
The situation is as follows: libTarget has a dependency on script automoc_target. In fact, automoc_target generates only 1 file, but for some reason Xcode decides to rebuild _completely_ everything that depends on automoc_target, and further down the chain (everything that depends on target that depends on automoc_target). Where to dig?