Cluster bombs are great for targets that are in a concentrated area, unfortunately the likely space targets aren't grouped in a cluster. Cluster bombs are more of a "gee, I hope we hit something" weapon when it comes to outer space.
The current spacecraft the United States has, the Boeing X-37B is a much more logical weapon.
http://www.dodbuzz.com/2010/12/03/what-could-x-37b-do/