iPhone 6 Photo stream deleting
It depends - if the photo is out of the Photo Stream Window and your deletion included the message that "this photo will be deleted from all devices" then yes - one delete wipes it forever.

If not, you may need to clean things up using iCloud.com and/or wiping your entire photo stream once you have the photos you wish to keep stored outside photo stream.

You can review the basics on cleaning up Photo Stream here:


How do you erase pictures from the Photo Stream album on an iPhone running iOS 5?


Things have changed since then and you have more options:

If you have sensitive photos, you can add them all to a hidden album. That places them in a "no thumbnail" / no preview state. If that's not enough, look over your current Deleted Items online directly from the cloud using https://www.icloud.com/#photos

That way, you know you are working with the authoritative version of all photos stored in iCloud.


Delete anything you don't need from deleted items to make sure your account is working and make it easy to permanently delete the offending images you want really purged.
Delete the images you want - follow up with purging them from Deleted Items.
Check your devices to make sure they followed the cloud deletion and don't have any stragglers.


Pay attention to the message that arrives when you delete an item. If it says it will be deleted on all devices, you know that device is in sync. If not, you will have to patrol all devices. This is easier by going to Settings - https://www.icloud.com/#settings - and making a check list of all the devices that could have your Photos from the stream.