Asp.net - Object References And Cache

I have a function GetAllProducts() which fetches all products from a database and stores it in the cache for future requests. This works fine, but if I then call the function e.g. ProductSearchResults = GetAllProducts(), and then modify ProductSearchResults variable, this also modifies the cache, which is very important this never happens, as the cache affects the whole website.

I understand this is because both ProductSearchResults and the cache now have the same reference, but how do I solve the problem? Is there something that I can put in GetAllProducts() to ensure the cache always uses its own value?

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