Edit: When I posted the question, I was thinking more on the line's of Feyman's theory that each photon simultaneously travels through infinite possible paths and thus knows the places where it is not supposed to land. This is why we see double slit interference even if we try sending one photon...
I might be mistaken, but say you have two independent sources with same color and may be polarization and the same phase even then they should be coherent.
If you have two similar coherent sources which are separated from each other by a barrier. Now one source sends particles one by one into one slit and the other sends particles into the other in a double slit interference experiment.
Now, the photons are always undistinguishable, so they should...