In the sense of being consciously modeled on Silicon Valley, copying many of the practices, I think it's fair to call some other tech scenes offshoots. New York I'd call different in that it's very media- and finance-heavy and leans on existing business tradition more. But even in NYC I can think of some companies that strike me as much more SV in culture than the NY median. And Seattle I don't know well enough to say.

Broadly, though, there are a ton of places that are (or would very much like to be seen as) Silicon Valley offshoots. Wikipedia lists dozens: https://en.wikipedia.org/wiki/List_of_technology_centers