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Set the Static or Smart Group to which you want this policy action to apply on the "Scopes" tab. The groups you add to this tab are CUMULATIVE, meaning that adding two groups to scope will include all computers from BOTH groups. If you want to only include those computers in common between both groups, create another Smart Group and choose two "Computer Group" criteria and set each of the them to the groups you want, and then choose the logical "AND" operator. "AND" will choose the "UNION" of both groups, meaning where they overlap/intersect.
Self Service
To be written...
User Interaction
To be written...