driving_site hint

 In a true distributed query, the optimization is done on the sending site. 
 Because your local site may not have access to the CBO statistics on the remote site, Oracle "punts" and does a full-table scan, and this is likely the cause of your full scan.

The driving_site hint forces query execution to be done at a different site than the initiating instance.
This is done when the remote table is much larger than the local table and you want the work (join, sorting) done remotely to save the back-and-forth network traffic.

select /*+DRIVING_SITE(r)*/
   columnNames,.....
from
  localTable        l,
  huge_Remote_table@dblink_xyz r
where
   l.columnName_XX = r.columnName_XX;