Apple has sent an email to registered developers notifying them of a complete wipe of CloudKit databases. The erase, which is scheduled to take place on July 22nd, is related to the iCloud APIs introduced at WWDC this year and will effect iCloud containers with public databases.
This is the second time Apple is deleting iCloud server data, as the tech giant performed a similar wipe on July 7th in order to upgrade their servers to coincide with the latest beta releases for iOS 8 and OS X Yosemite.
Here is Apple's full email to developers: