One was in Eastern China and one was in the Indus valley around what is now Pakistan and western India. They were at different time periods. See:
http://world-history-education-resources.com/indus-valley-civilization/chinese-comparison-civilization-indus.html
Did the Indus civilization get along with the Shang civilization?
(i have to provide the answer to this question , and a citation so would appreciate the help)
4 answers
so they never knew about each other?
I could not swear to it, but surely not a lot of back and forth. Look at the times in that link I sent you and look where they are on the globe.
The silk road and Marco Polo came a whole lot later :)