If someone wrote a "hello world" thing (class/type/whatever aka thing) and wanted everyone in the company to have and use it logically the creator ("you" in this example) would put it in the highest possible scope, right? That scope would be company-wide, right? What is company wide; well its the domain.
So if this company was "msdn.com" and you worked for channel9 and for simplicity lets say channel9 inherits all from the parent company. In other words placing hello world at msdn.com would give everyone at channel9.msdn.com the "thing" as well.
All tech questions have a catch, which I call "depends" (just like the diapers its a catch all). So the depends answer is based on the trust levels between domains. (Note sure if any of this is legally true, but just run with the example to illustrate the concept.) Basically, since channel9 is a sub-company of microsoft (aka microsoft.com) the trust between domains dicates how hello world could be passed there as well. However, it would not go to "apple.com" for it is limited to domains.
Hope that made any sense.
Workflow diagram are different in that you could use domain specific language (dsl) to create the rules that the workflow must follow or modify any aspect of it. Think of it like the tool used to create the workflow foundation. The depends is based on the eulas and I have no clue if it was created with it, but that is its level of power. Hope that helps...