One of the interesting features of Nexus is that it can interact with mirrors of remote repositories. Nexus will download artifacts and POMs from the mirrors you select, but it will download "secure" artifacts like checksums, MD5/SHA1 hashes, and PGP signatures from the original repository location. In addition to supporting mirrors of proxy repositories, Nexus also allows you to configure a list of mirrors for your hosted repositories.
If you want to learn more, watch this quick demonstration of the Mirror support in Nexus: