You are both wrong and right! Wreong to say that the tamil version copied from the bourne trilogy and right to say that ghajini copied the tamil version.
Ghajini is directed by the same person who directed the Tamil movie, thereby making it a remake in Hindi! the Tamil version picks up the basic plot from the critically acclaimed independent movie Memento byChristopher Nolan. In the Bourne Trilogy the protagonist does not suffer from short term memory loss, rather, his memory is erased because of the experiment.