Why?

Aurora Global RDS clusters are really nice things to have in AWS. They'll keep your RDS setup in sync between multiple, globally dispursed datacenters for you and all the positives that come with it. However, when you need to clean up an old setup after mgiration, they can be a pain to delete from the command line with the aws cli. Here's the steps you'll need, in the order you'll need them to get it done.

Steps

Remove your local cluster from the global one:

aws rds remove-from-global-cluster --profile <privileged_profile_name> --region us-west-2 --db-cluster-identifier <west_2_cluster_arn> --skip-final-snapshot

Find your list of instances for this region:

aws rds describe-db-instances --profile <privileged_profile_name> --region us-west-2 

Delete each one:

aws rds delete-db-instance --profile <privileged_profile_name> --region us-west-2 --db-instance-identifier <instance_id_found_above>

Delete the local cluster:

aws rds delete-db-cluster --profile <privileged_profile_name> --region us-west-2 --db-cluster-identifier <west_2_cluster_arn> --skip-final-snapshot

Do the other cluster:

aws rds remove-from-global-cluster --profile <privileged_profile_name> --region us-east-1 --db-cluster-identifier <cluster_arn> --skip-final-snapshot
aws rds describe-db-instances --profile <privileged_profile_name> --region us-east-1 
aws rds delete-db-instance --profile <privileged_profile_name> --region us-east-1 --db-instance-identifier <instance_id_found_above>

Delete each local cluster:

aws rds delete-db-cluster --profile <privileged_profile_name> --region us-east-1 --db-cluster-identifier <east_1_cluster_arn> --skip-final-snapshot
aws rds delete-db-cluster --profile <privileged_profile_name> --region us-west-2 --db-cluster-identifier <west_2_cluster_arn> --skip-final-snapshot

Delete the global cluster:

aws rds delete-global-cluster --profile <privileged_profile_name> --global-cluster-identifier <global_cluster_id>

Done!