Remember: If only some of your Domain Controllers are Global Catalogs make sure that the domain controller that holds your Infrastructure FSMO role1 is not a Global Catalog. The reason for this is that a global catalog that holds the infrastructure master role will stop looking for and removing phantom objects in your directory since it will have no phantom objects (we all know global catalogs hold partial information on every object in the directory) because it knows about every object in the directory if even a little.
However, if all your domain controllers are global catalogs, then it doesn’t matter where the infrastructure master lies since all domain controllers will know about everything in the directory and will (unless there are bigger problems) have accurate information about your directory objects.
Notes
1. http://support.microsoft.com/kb/197132