1. A computer program product for executing a Start Subchannel instruction in a computing environment comprising main storage and storage class memory, said computer program product comprising: a non-transitory computer readable storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising: based on determining that a subchannel identified by the Start Subchannel instruction is an Asynchronous Data Mover (ADM) subchannel, performing: obtaining an operation request block from main storage, the operation request block comprising an address of an operation block; based on the address of the operation block, obtaining the operation block from main storage, the operation block consisting of a request block, a response block, and one or more first move specification blocks (MSBs), wherein the request block comprises an MSB count field having a value indicating a number of MSBs associated with a request associated with the operation request block, wherein the response block is configured to hold exception conditions, wherein each move specification block is configured to include an operation code field, a block count field, a main storage address field for addressing main storage, a storage class memory address field for addressing storage class memory, a block size field and a flags field; obtaining a move specification block of the one or more move specification blocks; determining based on the operation code in the obtained move specification block an operation that the obtained move specification block is configured to perform on blocks of storage class memory; based on the move specification block, initiating the operation on the blocks of storage class memory associated with a storage class memory address of the storage class memory address field; and based on at least initiating the operation and encountering an exception condition, storing information within the response block, wherein the response block comprises an exception flags field, a field validity field, a failing MSB address field, a failing indirect data address word (AIDAW) address field, a failing main storage address field and a failing storage class memory address field, the information relating to one or more exceptions resulting from the operation, wherein the one or more exceptions are related to at least one of: main storage associated with a main storage address of the main storage address field, storage class memory associated with a storage class memory address of the storage class memory address field, or the obtained move specification block, and wherein the information includes an indication of an exception and additional information relating to the exception, the additional information specifying one or more address exceptions.