I have a feeling this has a speed increase. It's a Guttman-Rosler Transform, which means that the sorting is done by the native sort(). Also, I only reverse each key twice, whereas your method is probably doing a lot more reversing. 
@by_domain = 
  map { scalar reverse }
  sort
  map { scalar reverse }
  keys %hosts;

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japhy -- Perl and Regex Hacker

In reply to Re: Sort a long list of hosts by domain by japhy
in thread Sort a long list of hosts by domain (code) by deprecated

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