1. A method of reconfiguring a computing environment, said method comprising: determining, by a processor, that a configuration architectural mode facility is installed in a computing environment that is configured for a plurality of architectural modes and has a defined power-on sequence that is to power-on the computing environment in one architectural mode of the plurality of architectural modes, the one architectural mode comprising a first instruction set architecture and having a first set of supported features; based on determining that the configuration architectural mode facility is installed, reconfiguring, by the processor, the computing environment to restrict use of the one architectural mode, wherein the reconfiguring comprises: selecting a different power-on sequence to power-on the computing environment in another architectural mode of the plurality of architectural modes, wherein the another architectural mode is different from the one architectural mode, and the another architectural mode comprises a second instruction set architecture and having a second set of supported features; and executing the different power-on sequence to power-on the computing environment in the another architectural mode in place of the one architectural mode restricting use of the one architectural mode.