use strict;
use warnings;

my %hoa = (
    array1 => [ 1,2,3 ],
    array2 => [ 7,8,9 ],
    array3 => [ 1,2,3 ],
    array4 => [ 7,8,9 ],
    array5 => [ 9,9,9 ],
    array6 => [ 1,2,3 ],
);

my %counts;
while (my ($k, $v) = each %hoa) {
    push @{$counts{join '|', @$v}}, $k;
}

print "Duplicates:\n";
for (keys %counts) {
    next if @{$counts{$_}} < 2;
    print join ', ', @{$counts{$_}};
    print "\n";

}
__END__
Duplicates:
array1, array3, array6
array4, array2