1. A method of performing an inventory scan of target data processing systems for ascertaining the presence therein of prerequisite resources, wherein said prerequisite resources are resources necessary for the execution, by the target data processing systems, of predetermined activities, the method comprising: upon sending to a target data processing system a request of performing a selected activity of said predetermined activities, associating to the request at least one signature of at least one prerequisite resource different from the prerequisite resources required for performing the selected activity, wherein said signature includes information allowing the target data processing system to locate where the prerequisite resource is to be searched; and upon receiving from a target data processing system a result of the search of the prerequisite resource, updating information of presence of the prerequisite resource in the target data processing system.