You force summoned or called creatures back to where they came from. You can banish up to 14 HD of such creatures. For each additional Hit Die of creatures you banish, increase the Knowledge (arcane lore) check DC by +1. To banish a creature that's not summoned or called, increase the Knowledge (arcane lore) check DC by +6 if the
target creatures are limited to elementals and outsiders, or by +10 if the
target creatures are of a different type.
In general, creatures return whence they came. Some creatures, such as vivilors, return to the edge of Shadow. Elementals fade into nothingness, their elemental nature suffusing and dispersing throughout the immediate area. Outsiders likewise disappear to a place beyond Shadow, though some eventually find their way back with dim memories of their previous sojourn in the mundane world. Other creatures simply reappear wherever they were before they were summoned.