The problem with the term "civilization" is that we only use it because it doesn't actually mean much.

When we talk about the Indus Valley civilization, it's really because we have no better term. We know there was some continuous cultural tradition, distinct from its neighbors and with some form of associated government and language. We might be better off saying "culture" or "society," but even these words are really just ways to refer to any large culturally-bound group of people.

We call it "Egyptian civilization" not because we don't know enough about it to call it something more specific, but because we're referring to two thousand years of a consistent cultural tradition. We might say "Egyptian kingdom," but that leaves out Intermediate periods of civil disunity and later occupations by Greece and Rome. Similarly, with Ancient Greece, calling them "the Greek city states" sounds much too political and leaves out the Hellenistic period, but they weren't quite an "empire" until that period.

Whenever a question about categorical civilizations pops up, we must ask "What's isn't a civ?" Some will argue that groups without urbanization or a state aren't, but that's a dated and often Eurasia-centric definition. It's a term rarely used in the social sciences any more, and even then only in the broadest and most general context as a non-operative word for some complex of culture-politics-language-etc.