IdMapping is used by the deep clone operation to map ObjectIds between original objects and their clones (using IdPairs). 

Autodesk.AutoCAD.DatabaseServices.IdMapping

Public sealed Class IdMapping
Inherits RXObject
Inherits IEnumerable

public sealed class IdMapping : RXObject, IEnumerable;

There is no method provided to clear all entries in an instance of IdMapping. A new instance must be created for each use in a deep clone operation. Making IdMapping unique for each deep clone operation makes it possible to use the instance address as a distinguishing identifier in deep clone notification. 

IdPair instances that have been added to the map are destroyed when the IDMapping instance is destroyed. 

IdPair, Database.DeepCloneObjects, Database.AbortDeepClone, DBObject.DeepClone, DBObject.WblockClone