How do I make a rule to ignore or delete messages that are cross posted to
several news groups at one time? I only want to see the ones posted to the
single newsgroup subscription of mine.

example I subscribe to alt.blue.lovers
someone post to alt.blue.lovers; alt red.lovers; alt.yellow.lovers.
I want an easy way to eliminate this cross posting threads because they will
have replies form all three newsgroups and i have nothing in common with red
or yellow lovers.