Event reciver that after a fields updating , update a field in a list in another Site

Hi ,

i have 2 list  :List A  with  column from 1  to 5 ,List B with column from 1 to 5 , but List B is an another Site . I want to do a event reciver that  if  a field in in List A  change update the same field in List B.

How can specify the trigger fields to start the event reciver for example  the field 3 and 4 where the field 1 is equals somethings? with a query?

Thank you