purple flowering tree

I saw this tree today in the Albuquerque Rose Garden, and got this shot, but had no idea what it was. I did an image search and it said it was a Vitex tree, also known as a Chaste tree or a Texas Lilac tree (but I don't think it's related to the actual lilac family). But if anyone knows more about this tree, please feel free to add any information in comments.

Done