“Cleaning” appears when your device is clearing the app's cache, which is a temporary storage area for documents and other data. You don't need to do anything: just wait for the word to go away, which means the process is complete. No data is lost during cache cleaning, because your documents are stored on iCloud.

After the cache is cleared, document icons in the iWork app may be dimmed and show a download arrow. Tap the document to download and open it as normal. If you can't open the document, contact iCloud Support for help.

More information about cache cleaning
On devices using iOS 5 or later, cache cleaning occurs automatically when the device has less than 1 GB of available storage. This storage-management feature is designed to optimize the performance of your iOS device when space is limited. The cache for infrequently used documents is cleared first.