How to clear all unread notifications ?

Question

I have 3.341 unread notifications and I want do clear them all at once. 
 If I click on Unread button and choose Mark as Read it clears only 10 of them.

ruckus · Accepted Answer

The cause of this is because the subscriptions function was set to subscribe you to all threads in a group if you joined that group. We changed that by removing subscriptions and making sure future subscriptions are only to threads you have created, posted to, or actively subscribed. I'm aware of the issue with the notifications and I'm looking to see if we can get the them cleared down for all users without you having to do anything.

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Communities Moderator, SOPHOS
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ZeusDionysos · Answer

Nice, all my unread notifications disappeared! 
Thank you!