Motivated by the recent detection of gravitational waves from the black hole binary merger GW150914 , we study the dynamical evolution of ( stellar mass ) black holes in galactic nuclei where massive star clusters reside . With masses of \sim~ { } 10 ^ { 7 } ~ { } M _ { \odot } and sizes of only a few parsecs , nuclear star clusters are the densest stellar systems observed in the local universe and represent a robust environment where black hole binaries can dynamically form , harden and merge . We show that due to their large escape speeds , nuclear star clusters can retain a large fraction of their merger remnants . Successive mergers can then lead to significant growth and produce black hole mergers of several tens of solar masses similar to GW150914 and up to a few hundreds of solar masses , without the need of invoking extremely low metallicity environments . We use a semi-analytical approach to describe the dynamics of black holes in massive star clusters . Our models give a black hole binary merger rate of \approx~ { } 1.5 ~ { } Gpc ^ { -3 } yr ^ { -1 } from nuclear star clusters , implying up to a few tens of possible detections per year with Advanced LIGO . Moreover , we find a local merger rate of \sim~ { } 1 ~ { } Gpc ^ { -3 } yr ^ { -1 } for high mass black hole binaries similar to GW150914 ; a merger rate comparable to that of similar binaries assembled dynamically in globular clusters . Finally , we show that if all black holes receive high natal kicks , \gtrsim~ { } 50 ~ { } km~ { } s ^ { -1 } , then nuclear star clusters will dominate the local merger rate of binary black holes compared to either globular clusters or isolated binary evolution .