The IRS has the power to make almost anything that your name is on. A good rule of thumb for this is that if you can access the funds, so can the IRS.
Even though creditors cannot touch your retirement accounts, the IRS can seize your pension, 401k, and any other retirement accounts that you have. If you do not have access or rights to these funds, such as if your employer owns the fund and you do not have access, then the IRS cannot levy the accounts.
Any inheritance funds in estate accounts that are not distributed should not be accessible to the IRS. Yet, that does not mean that it cannot be levied. The IRS can seize part of your inheritance to settle your tax debt. Once the inheritance has been placed in your name, then the IRS can levy those assets. For more information, please read our article on what can the IRS seize for your back taxes.