Let me start by saying, this should never be done. never. Ok, that aside, i thought of a way that might work.
     You could loop through the %main:: hash, and compare the values of each name-spaces hash variable. Something like this (untested code and idea):

%hash1 = ('A' => 1);
$href = \%hash1;
foreach my $name (keys %main::) {
    if ($href eq \%{"main::$name"}) {
        print "Hash ref is for %",$name,"\n";
    }
}
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Please note, i do not condone this behavior.

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from the frivolous to the serious