I have 55,000 records I need to delete from the All Subscribers List. It seems like the only obvious way to do this is by selecting all and deleting page by page.
I will appreciate pointers on a more efficient method.
After a month long tussle with Marketing Cloud Support, I was finally able to resolve this.
Our current set up is an Enterprise 2.0 account. The recommended method was to export the All Subscriber List to a list and delete the list, while check the option to delete this from all applications.
Problem is that although the UI gives you the option to do this, it is a bug. You cannot delete the All Subscriber List from the Business Unit Level.
I had to switch to the enterprise level and import the All Subscriber List here to delete it.
You could achieve this using a custom script/program in the language of your choice that communicates with the Marketing Cloud SOAP-API. The SOAP-Envelope you need to use to delete a subscriber can be found in the Marketing Cloud Documentation: Deleting A Subscriber
For an alternative solution: If there is any common trait around these subscribers or you are looking to remove ALL your subscribers, you can create a Group (filtered list) on these subscribers based on any Profile Attribute. Then when you delete the group, it will ask you if you want to delete them from the account entirely, which will remove them from the All Subscribers list.