Perl doesn't have "garbage collection" in the sense that it never gives memory back to the OS.
Once Perl has memory from the OS, it has it forever.
A long-lived Perl app will reach a maximum memory usage and just stay at that number forever (provided no memory leaks).
If you un-define an object ref: $obj_a = undef;
$obj_a = Method_X->new(...), reuse/reassign an object ref that has the same effect as long as no reference to an in internal structure within obj_a is in existence.
Perl has its own memory management and reuses memory when it can.