use strict;

my %hash = (
   Key1 => [qw(a b b b a a c d b d b)],
   Key2 => [qw(c a b a b d c c d d d e f)],
);

for (sort keys %hash) {
   my %counted;
   $counted{$_}++ for @{$hash{$_}};
   print "$_:\n";
   for (sort { $counted{$b} <=> $counted{$a} } keys %counted) {
      print "\t$_ = $counted{$_}\n";
   }
}