From what you are describing it seems you are using Indexing V1. So from what I know you would really have two options which the first one would be to upgrade your clients to Indexing V2 (Upgrading Clients to Indexing V2) and if that is not an option right now, you can build a Secondary Index Server.
For Secondary Index Server refer to: https://documentation.commvault.com/commvault/v11/article?p=10715.htm
The indexing retention service for V1 will run every day and clean anything older than 15 by default. You can configure the retention as well, see the link https://documentation.commvault.com/commvault/v11/article?p=10713.htm
Index Version 1 Diagram https://documentation.commvault.com/commvault/v11/article?p=10709.htm
Index Version 2 Diagram https://documentation.commvault.com/commvault/v11/article?p=10774.htm
I`m just a CV user, there are some Pros here that im sure can shine a light to you as well.
Hope that helps.