See which remote databases are using a ‘materialized view log’ on source database with:
SELECT mview_site , COUNT(*) FROM dba_registered_mviews GROUP BY mview_site ORDER BY 1 ;
The snaptime$$ column shows how old the data is in any materialized view log:
SELECT TRUNC(snaptime$$) , COUNT(*) FROM owner.mlog$_mytable GROUP BY TRUNC(snaptime$$) ORDER BY 1 ;
Oracle’s Interactive Quick Reference helped identify the dba_ views for this.