A software distribution is always sent to a single collection, but collections can contain resources in any number of sites. When SMS sends your software distribution to clients in more than one site, you need to consider the following issues.
You can originate a software distribution for a site and any of its child sites. SMS automatically sends packages down the site hierarchy. If a package originates in site A, the package appears in all site A's child sites as a locked package, which means that the originating site is always the owner of the package and has full control over all its settings. Child sites of the originating site can administer the package for themselves and any of their child sites but cannot override settings from the originating site.
Collections, packages, and advertisements are automatically replicated to child sites, but package source files are not. Because clients cannot cross site boundaries to gain access to distribution points, you must specify at least one distribution point for a package in each site containing clients that will receive the advertisement. Administrators in child sites can add and remove distribution points for their site and child sites. However, these administrators cannot remove the distribution points specified by parent sites.
SMS copies advertisements and collections to child sites and reevaluates them at regular intervals. As resources in the target collections change, SMS modifies the list of resources that belong to the target collection.
Distributing Software to Clients
How Software Distribution Works
Distributing Software to Clients Overview