You want to view the sites a domain controller covers.
In the following command, replace <DomainControllerName> with the name of the domain controller you want to view site coverage for:
> nltest /server:<DomainControllerName> /DsGetSiteCov
Although you cannot use it directly from a scripting language like VBScript, Microsoft provides a DsGetDcSiteCoverage method that can be used by languages, such as Visual Basic and C++, to retrieve site coverage information. In fact, the nltest command shown in the CLI solution is a wrapper around this method.
Recipe 11.17 describes how to force a domain controller to cover multiple sites. Recipe 11.19 describes how you can disable a domain controller from covering for any sites other than its own.