You almost have to build a list of all the key-pairs, if you're asking what I think you're asking.

my @keys =
    sort { $bdry{ $b->[0] }{ $b->[1] } <=> $bdry{ $a->[0] }{ $a->[1] }
+ }
     map { my $k = $_; map { [$k, $_] } keys %{ $bdry{$k} } }
    keys %bdry;

print "my greatest key-pair is: $bdry{$keys[0][0]}{$keys[0][1]}\n\n";

print "key-pair(@$_) is: $bdry{$_->[0]}{$_->[1]}\n" for @keys;
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UPDATE: I'm glad this is was exactly what you wanted. Normally I try not to answer the entire question with code, as that takes a lot of the fun out of it; but in this case there wasn't really an easier way to say it.