Script to find invalid synonyms

select *  
from dba_synonyms s  
where table_owner not in ('SYS', 'SYSTEM')
and db_link is NULL  
and table_name not in 
    (select object_name
    from dba_objects o
    where o.object_name = s.table_name
    and o.owner = s.table_owner
    and o.object_type not like '%SYNONYM%')
order by owner asc;