It's also observable on the scale of galaxies. Evidence for dark matter includes observed inconsistency between galactic rotation curver and total mass estimates. But yes, some of the earliest evidence (decades of it) was unexpected behavior of galactic clusters.

Anyway, what we expect to see here is what's typical at our distance from Sagittarius A[star], and distance from the galactic plane.

Also, I gotta say that the galactic dark matter distribution reminds me a lot of Vinge's "Slow Zone" ;) A Fire Upon the Deep came out in 1992. I wonder whether he had dark matter in mind. He never used the term, as I recall.