The "snmp ifindex persistence" interface configuration command enables and disables ifIndex persistence for individual entries (corresponding to individual interfaces) in the ifIndex table of the IF-MIB.

-- So the above command is on a per interface basis

The "snmp-server ifindex persistence" global configuration command enables and disables ifIndex persistence for all interfaces on the routing device (this applies only to interfaces that have ifDescr and ifIndex entries in the ifIndex table of the IF-MIB).