While grey goo is about matter, this appears to be a grey energy scenario: one where machines run amok eating all possible energy in an exponential feedback loo

While grey goo is about matter, this appears to be a grey energy scenario: one where machines run amok eating all possible energy in an exponential feedback loop of uselessness, driving civilisations to oblivion. While the civilisations are long-gone, they build up the Kardashev ladder for the sole purpose of producing more of nothing. Finally, all cosmic resources being expanded, they shut down. Since nobody remained to observe, it is unknown whether in a brief flash of self-awareness, realising the meaninglessness futility of their existence, the machines commited suicide.