Thank you everyone for your replies and comments. It has been an interesting discussion.

I actually used zentara's suggestion of forking the large memory section so that once the process ended, the memory was returned. This works well and as I was already using Parallel::ForkManager elsewhere in the code I only had to make a couple of changes to the code so thank you!

For those interested, in addition to following Anonymous Monk's advice and passing the $coverage hashref as an argument to the sub, the other changes I made to get this working as I want were as follows:

• Initially adding the use of Parallel::ForkManager and configuring a max of 1 fork

use Parallel::ForkManager;
my $fm = Parallel::ForkManager->new(1);
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• Inside the foreach loop identify the code to be run within the fork and initiate the fork

foreach my $t (@times){
 $fm->start and next;
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• At the end of the loop, identify the end of the code within the fork and finish the fork. Outside the loop, block the main process until the forked process has finished.

 print "what's the mem doing?\n";
 sleep(10);
 $fm->finish();
 }

$fm->wait_all_children();
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That's it. The forked process releases the memory when it finishes and the next process starts afresh.

Cheers,
Rich