package Whatever;

sub new { my $self = 0; bless \$self } # $self is Whatever=SCALAR(0x9742b30)
sub blah { my $self = shift; say $self }

package main;

my $a = Whatever->new;
my $b = $a;

# I want to kill $a such that $b is now also undef.  How?
$a->blah;
$$a = undef; # I really want to undefine ALL references to Whatever=SCALAR(0x9742b30)
$b->blah; # This should die.